Broach marks

[Michael G.]

Could someone please give me a crash course on broach marks. What they are, Where they are, and how they should appear on an unaltered pad. Thanks.

Mike

[Patrick H.]

Re: Broach marks

Michael,

What - Longitudinal machining lines on the engine's stamp pad.

Why - When the block was decked at the factory, the blades left these lines. If you've ever scraped items with a razor blade you've noted that the blade gets nicked over time. In a similar manner, worn blades caused deeper "broach marks" on some pads.

How - can appear from "invisible except with magnification" to rather deep. My originals are shown below. See enough examples and you'll begin to tell apart real from fakes with reasonable certainty.

Patrick.

[William C.]

Re: Broach marks

They are describing the normal result of any machining process involving the use of a cutting tool on metal, but the specific machining process is the use of a "Broach" in the Flint or Tonawanda Engine plants. In the case of the engine block, the machining process was performed over a distance of 20+ feet by pushing the unmachined block through a series of cutters to cut the block deck surfaces and the main bearing surfaces at the same time. Beacuse the machine was stationary, and the block moved horizontally the machine marks run parallel to the crank centerline in a consistant front to back pattern. As no typical machine shop has the equipment used in Flint, rebuilders typically machine block durfaces by clamping the block onto a register surface and using a rotary cutter that moves across the top of the block deck surfaces leaving a circular path where the cutter does its work. It's sort of a "one look beats a thousand reports" situation, but I hope you can envision it from this description.

[Michael G.]

Re: Broach marks

Gentlemen,

That was the most complete and thorough explanation I could have hoped for. Thank you. Patrick, your photo was awsome. Markings were distinguishable. Thank you guys, as always.

Mike

[Rainer S.]

Re: Broach marks

When GM (and other of the "Big Three") machined the engine block from a raw casting, they would load the engine block, as it came from the foundry and load it into a huge broaching machine the size of a 10-wheeler truck, but wider.
The engine block was loaded into a fixture, tipped 90 degrees, with the (2) cylinder bank faces to one side and the bottom, where the crank shaft goes, to the other side (I don't remember which side was to the right or to the left).
The clamp fixture would locate the block at various places on the rough casting and specifically on the cylinder bore sleeves, to assure proper stockremoval.
The block would then be pushed thru the entire lenght of the machine by a large hydraulic cylinder, called a ram. This took approx. 20 to 25 sec, loading machining and unloading.
On both sides of the "tunnel", thru which the block would travel, there were large clusters of so-called "broaches", which looked like angular chissels, inches wide and thick. These "broaches" were stationary. The block would travel along the staggered broaches the entire length of the machine.
As the rough casting travelled, pushed by the large hydraulic shaft, the broaches, being staggered progressively, would "shave", or "broach") the casting, removing approximately 1/8 to 1/4" from the (2) cylinder bank faces, the intake mounting faces and the crank shaft mounting face, to finished dimensions.
The broach action caused the bank faces, of which the engine pad is part of, to leave behind what we know as "broach marks".
Since the machining action of the broach tools is so unique, being stationary and almost perpendicular to the moving engine block during machining, it can virtually not be duplicated by other methods.
I remember seeing these machines at Buick and Chevrolet in Flint, as well as Ford in Dearborn and Cleveland. They all used the same "Block Broaches" at the start of the engine machining line.(Made by Ex-cello ??) Quite a sight to see them in action, as well to hear them. In later years they were enclosed to keep the sound and dust inside the machine).
I used to work for Machine Builders who build the machines after the broach.
These broach marks look like uneven score marks. When looking at the engine pad, you should see these marks. If you would take off the heads, you should see them along the entire face, where the cylinders are. (inline with the direction of travel of the car).

Sorry for the lengthy answer to your question...

Rainer

http://rschwager6855@sbcglobal.net

[Terry M.]

Re: Broach marks

I recently (at the judging retreat) saw a 1955 press release on the opening of the Flint engine plant. It described in far better words than I can the process. Unfortunately the member who has it would not make a copy for me, but assures me he will produce a story for Vinnie for The Restorer. That was a remarkable place when it opened, and I think they produced something over 59 million engines and partial engines before it closed.

You almost had to see those machines and the transfer line that brought the cylinder case castings there and shuttled them off to the next operation. Metal working is often a very primitive process, and this part of it was very primitive. Smoke rose from the cutting surface -- with no lubricant. And the noise was overwhelming. Flint had five of those Cincinnati broach machines -- each about 75 feet long and 20 feet wide. I tried to take a picture the one time I was allowed a camera in there, but there wasn't enough light. Everything was covered with cast iron dust, and that just sucked all the light.

You can see the marks on the cylinder head and the lower intake surface -- those were all cut at one time. The case then flipped over and the oil pan rail and the upper half of the main bearing surfaces were cut. The case is held stationary and the cutting tool -- like a giant file -- is drawn across the surfaces. The tooling is about 40 feet long and ten feet high. It cuts the top of one case and the bottom of another at the same time. The stroke of the tool was about 30 feet.

[Rainer S.]

Re: Broach marks

While I was writing my answer, I was sidetracked, and didn't realize, till after I posted, that Pat and Bill also answered...

Rainer

[Michael G.]

Outstanding education-Thanks to all *NM*

[Rainer S.]

Re: Broach marks

Terry, thanks for correcting my recollection of the process. I thought, the block was pushed thru the broaches, but reading your description, the broaches actually moved. It was the lader which was advanced by a hyrd. cylinderinto the machine, than the braches took over. (It's been a long time, since I saw these machines, some 35 to 40 yearsa).
You could actually taste the cast iron, while working in the plant. I worked for Cross and later La Salle. Cross made the engine block metall removing machines. (besides Kingsbury and a few others).
The entire engine block is machined dry, with the exeption of honing the cylinder bores, for which they used a special honing fluid. I still can't believe they would let us work under those conditions back then. Now all machines are enclosed in floor dry guarding and the fumes are sucked away and filtered.
Looking forward to read the article in the Restorer...

Rainer

[Mark G.]

Re: Broach marks

The Flint, Tonawanda, and St. Catharines vertical broach machines were a large because they did two operations. It surfaced the pan rail and bearing cap/crank channel then the head contact face (left & right banks) including the manifold rails.

The cylinder & case was loaded on the conveyor rear housing first pan rail down. The first operation flipped the block upside down on the “A” casting locators (3 pts.) and the ”B” locators (2 pts.) on the oil filter side. It was clamped in the fixture and rotated 90 deg. into position and the broach would make a cutting pass across the casting.

The second operation transferred the block to the next fixture flipping it again to locate on the new broached surfaces. Pan rail for the plane and cap/crank channel for a centerline; then clamped and rotated 90 deg. into position for the return pass on the head contact faces. This was a rear to front cut; because when the rear manifold rail (China Wall) broke it was toward the tappet valley side. These two operations were engineered to transfer the surface dimensions from the cast locators to a machined surface on the cylinder & case.

This was a dry machine cut using a calculated progressive chip load rate removing .125” to .200” in. (.180” nominal) of cast iron. The broach blade inserts were configured to produce the required shape and surface finish. Two foundry/casting conditions affected the tool inserts, metal hardness and surface scale. Hard cast iron (chilled) could break the blades; scale is the work-hardened (shot peened) skin the front blades broke through to get to the good iron.

The third operation was the bank stagger (front to rear) equalization. Probes located the center water jacket holes in each bank (.880” stagger) clamped the casting and drilled/reamed the manufacturing locators or gage holes. The remaining machining used these holes and the pan rail for positioning.

Mark #35760

[Joe L.]

Re: Broach marks

Mark-----

GREAT information! Thanks!

[Terry M.]

Re: Broach marks

Rainer,
I saw three of the five Flint machines. Those three were Cincinnati brand and worked as I described. The other two could have been different. I think I saw them starting in 1985 -- we celebrated the 30th anniversary of the small block at our national convention in Boston -- complete with a slide presentation by one of the developing engineers. Later that summer when I toured Flint with the Chevelle Club (now defunct) they didn't even mention the anniversary.

When NCRS had the National in Warren one of the tours was of Flint engine. I managed, with the help of some other members, to make some friends there. Whenever they had open house for friends and family I would get a phone call or later an email. I often wonder what happened to some of those guys. The days when people spend their whole working career at one location are all but gone. The dedication of those guys, and the working conditions were something.

At Flint they used to torque the main and rod bolts by hand. To see it was marvelous. I think it was four or five guys moving around the upside-down case with a rhythm that allowed them to get to the rod bolts as one of them turned the crank. They did it for about 20 minutes and then got a break. They had teams that worked together in order to keep up the rhythm. When I noticed they began to use a machine to torque rod an main bolts, I was told it was to reduce the human damage that the repetitive tasks caused -- the same reason they stopped steel stamping the assembly codes after the Gen I build-out.

I also saw the broach machines at Tonawanda, but I can't recall details of those machines -- I was too in awe of their size and operation. I wrote a story for The Restorer about that trip -- it was just as the Mark IV line was closing, and I think the horizontal broach was on its last use there.

It is a far cry from the assembly process at Wixom. We've come a long way.

[Kevin M.]

Re: Broach marks

Didn't any of you guys have a camera? Pictures please.

Kevin

[John H.]

Re: Broach marks

The photo below shows the two large master gage holes Mark noted that were used for subsequent machining operations - one at the front directly below the fuel pump boss, and the other at the rear, on the starter pad area. The machining pallets on the transfer lines had pins that located in these holes, and clamps to hold the pan rail area of the block down solid on the pallet.

[Terry M.]

Re: Broach marks

Kevin, I explained my attempts with a camera -- it was before digital camera's were common -- in my first post above. Most of the time photography in the engine assembly plants, just like in the Corvette Assembly Plant(s) is prohibited. In this case it would have taken a full professional lighting session -- that place was black as a well, and the sheer size of the machine makes lighting it a major production. I have, however, seen a picture of the broach machine, but I can't recall where. I believe it was in some technical publication, but since I work in automotive education I see a lot of publications. Keeping track of all them is a challenge.